In cellular communication, a user equipment (UE) existing in a cell accesses a base station to receive control information for exchanging data from the base station in order to perform communication and then transmit and receive data to and from the base station. That is, since the UE transmits and receives data via the base station, the UE transmits data to the base station in order to transmit the data to another cellular UE and the base station, which has received the data, transmit the received data to another UE. Since the UE must transmit data to another UE via the base station, the base station schedules channels and resources for data transmission and reception and transmits channels and resource scheduling information to each UE. In order to perform UE-to-UE communication via a base station, the base station needs to assign channels and resources for transmitting and receiving data to each UE. However, in D2D communication, a UE directly transmits and receives a signal to a desired UE without via a base station or a relay.
If UE-to-UE communication or D2D communication for directly transmitting and receiving data between UEs is performed by sharing resources with an existing cellular network, each UE may perform UE-to-UE communication after resource assignment for UE-to-UE communication. However, in communication between UEs using different frequencies, it is necessary to determine operating frequencies upon resource assignment. That is, one of first and second UEs, which subscribe to different communication operators, may move to an operating frequency of a peer UE for D2D communication or D2D communication is performed at a third frequency.